The purpose of this study is to compare the biochemical and mechanical changes taking place in the uterine and carotid arteries during pregnancy and following delivery in both normal and hypertensive animals. The studies will be done in pregnant rabbits, in rabbits pretreated with estrogen, estrogen and progesterone, and progesterone in order to separate the effects of these two hormones on the vasculature, and in rabbits made hypertensive by ligating on renal artery. A smaller number of experiments on pregnant and post-partum sheep are planned because many of the uterine vascular responses in the ewe are similar to that of the human. Intact arterial segments will be studied in vitro by placing them in a muscle chamber, cannulating both ends and subjecting them to cyclical application of pressure (inflation and deflation cycles) while the segment length is kept constant. Pressure, diameter changes and isometric force measurements moduli and impedance. Measurements of rates of protein synthesis and degradation, collagen and elastin, electrolytes and water will be used to interpret the mechanical changes.